The present invention relates to a light-emitting semiconductor device having a pn junction.
The known art abounds with light-emitting semiconductor devices. One example is illustrated in FIG. 11, in which light is emitted through an n-type gallium-arsenide (GaAs) substrate 11 by a vertical cavity laser comprising an n-type distributed Bragg reflector (DBR) 12, an active layer 13, and a p-type DBR 14, which are formed on the substrate 11. The device is driven by current flowing from a positive electrode or p-electrode 15, which makes contact with the p-type DBR 14, to a negative electrode or n-electrode 16, which makes contact with the substrate 11. The p-type DBR 14 has a mesa shape, formed by etching away material from the region 17 surrounding the mesa.
Compared with other light-emitting semiconductor devices, the device in FIG. 11 has the combined advantages of converting current to light efficiently, and emitting the light in a circular beam perpendicular to the surface of the device. The need for mesa etching, however, is a disadvantage. When an array of light-emitting devices must be formed on the same semiconductor substrate, for example, the need for mesa etching limits the density of the array. In addition, the irregular surface height created by mesa etching leads to problems that reduce the yield of the fabrication process. Specific problems include defocusing during photolithography, incomplete removal of photoresist material and electrode material, and electrical discontinuities in electrode lines.